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The Vulnerabilities Equities Process and the NSA

Software security flaw disclosure is a widely overlooked area of public policy, and that’s with it becoming more important every year. U.S. intelligence agencies failing to disclose critical security flaws that could significantly adversely affect citizens is generally subjecting the country to dangerous levels of risk. And as happens much of the time, it’s a similar story with other countries.

One could certainly condemn the Shadow Brokers, a group of hackers with links to Russia who stole and published the National Security Agency attack tools that included the exploit code used in the ransomware. But before all of this, there was the NSA, which found the vulnerability years ago and decided to exploit it rather than disclose it.

All software contains bugs or errors in the code. Some of these bugs have security implications, granting an attacker unauthorized access to or control of a computer. These vulnerabilities are rampant in the software we all use. A piece of software as large and complex as Microsoft Windows will contain hundreds of them, maybe more. These vulnerabilities have obvious criminal uses that can be neutralized if patched. Modern software is patched all the time—either on a fixed schedule, such as once a month with Microsoft, or whenever required, as with the Chrome browser.

When the U.S. government discovers a vulnerability in a piece of software, however, it decides between two competing equities. It can keep it secret and use it offensively, to gather foreign intelligence, help execute search warrants, or deliver malware. Or it can alert the software vendor and see that the vulnerability is patched, protecting the country—and, for that matter, the world—from similar attacks by foreign governments and cybercriminals. It’s an either-or choice. As former U.S. Assistant Attorney General Jack Goldsmith has said, “Every offensive weapon is a (potential) chink in our defense—and vice versa.”

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The particular vulnerability in WannaCry is code-named EternalBlue, and it was discovered by the U.S. government—most likely the NSA—sometime before 2014. The Washington Post reported both how useful the bug was for attack and how much the NSA worried about it being used by others. It was a reasonable concern: many of our national security and critical infrastructure systems contain the vulnerable software, which imposed significant risk if left unpatched. And yet it was left unpatched.

There’s a lot we don’t know about the VEP. The Washington Post says that the NSA used EternalBlue “for more than five years,” which implies that it was discovered after the 2010 process was put in place. It’s not clear if all vulnerabilities are given such consideration, or if bugs are periodically reviewed to determine if they should be disclosed. That said, any VEP that allows something as dangerous as EternalBlue—or the Cisco vulnerabilities that the Shadow Brokers leaked last August to remain unpatched for years isn’t serving national security very well. As a former NSA employee said, the quality of intelligence that could be gathered was “unreal.” But so was the potential damage. The NSA must avoid hoarding vulnerabilities.

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Can the NSA discover vulnerabilities that no one else will? Or are vulnerabilities discovered by one intelligence agency likely to be discovered by another, or by cybercriminals?

In the past few months, the tech community has acquired some data about this question. In one study, two colleagues from Harvard and I examined over 4,300 disclosed vulnerabilities in common software and concluded that 15 to 20 percent of them are rediscovered within a year. Separately, researchers at the Rand Corporation looked at a different and much smaller data set and concluded that fewer than six percent of vulnerabilities are rediscovered within a year. The questions the two papers ask are slightly different and the results are not directly comparable (we’ll both be discussing these results in more detail at the BlackHat Conference in July), but clearly, more research is needed.

People inside the NSA are quick to discount these studies, saying that the data don’t reflect their reality. They claim that there are entire classes of vulnerabilities the NSA uses that are not known in the research world, making rediscovery less likely. This may be true, but the evidence we have from the Shadow Brokers is that the vulnerabilities that the NSA keeps secret aren’t consistently different from those that researchers discover. And given the alarming ease with which both the NSA and CIA are having their attack tools stolen, rediscovery isn’t limited to independent security research.

But even if it is difficult to make definitive statements about vulnerability rediscovery, it is clear that vulnerabilities are plentiful. Any vulnerabilities that are discovered and used for offense should only remain secret for as short a time as possible. I have proposed six months, with the right to appeal for another six months in exceptional circumstances. The United States should satisfy its offensive requirements through a steady stream of newly discovered vulnerabilities that, when fixed, also improve the country’s defense.

The VEP needs to be reformed and strengthened as well. A report from last year by Ari Schwartz and Rob Knake, who both previously worked on cybersecurity policy at the White House National Security Council, makes some good suggestions on how to further formalize the process, increase its transparency and oversight, and ensure periodic review of the vulnerabilities that are kept secret and used for offense. This is the least we can do. A bill recently introduced in both the Senate and the House calls for this and more.

In the case of EternalBlue, the VEP did have some positive effects. When the NSA realized that the Shadow Brokers had stolen the tool, it alerted Microsoft, which released a patch in March. This prevented a true disaster when the Shadow Brokers exposed the vulnerability on the Internet. It was only unpatched systems that were susceptible to WannaCry a month later, including versions of Windows so old that Microsoft normally didn’t support them. Although the NSA must take its share of the responsibility, no matter how good the VEP is, or how many vulnerabilities the NSA reports and the vendors fix, security won’t improve unless users download and install patches, and organizations take responsibility for keeping their software and systems up to date. That is one of the important lessons to be learned from WannaCry.